Thin plastic film and sheet material are produced in many sizes and thicknesses for various applications. For example, smooth polyethylene film and sheet are put to such widely diverse uses as drop cloths, tarpaulins, moisture barriers, mulching and soil erosion control material, and, of course, they are widely used in the packaging and container industry. Indeed, agricultural, industrial and domestic uses of plastic film and sheet material are too numerous to mention.
One significant negative factor associated with the use of thin plastic film and sheet, however, is a tendency to tear under load. Of course, once a tear is initiated, it tends to extend across the entire sheet in greater or lesser degrees of repidity. This is particularly true in cases where the film or sheet is used in outdoor environments and exposed to wind and the elements, as in the case of tarpaulins, and landscaping, landfill, and mulching films.
It is the primary object of this invention to provide thin plastic film and sheet material which retains all of the benefits of conventional plastic film and sheet material, but which also minimizes or prevents the propagation of any tear which might form in the film or sheet.
In the present invention, thin plastic film and sheet material are formed with a plurality of integrally formed surface ribs which may be arranged in any number of configurations. For example, in the case of rectangular or square film or sheet, a series of laterally spaced, parallel ribs may extend from one end of the sheet to the other. In another embodiment, a criss-cross or lattice-type rib arrangement may be utilized. It is also contemplated that a diagonal, or diamond-shaped arrangement, as well as any other suitable rib pattern may be employed.
It will also be appreciated that the ribs themselves may be formed in various configurations. For example, all of the ribs may extend from only one of an upper and lower surface of the sheet; all of the ribs may extend from both upper and lower surfaces of the sheet; or, adjacent ribs may alternately extend from upper and lower surfaces of the sheet.
In addition, the ribs may have any desired cross-sectional shape, such as rectangular, square, semi-circular, triangular, etc.
The material used to form the film and sheet material is a plastic material, preferably high, medium or low density polyethylene.
In manufacturing plastic film and sheet material according to this invention, any conventional plastics forming technique such as blown film, extrusion and co-extrusion, may be used. Regardless of which technique is utilized, the resultant sheet or film is formed as a unitary article with integral ribs arranged as desired.
With respect to film and sheet thickness, it is sometimes stated that plastic material having a thickness of 10 mil or less is regarded as a "thin film", while material having a thickness over 10 mil is regarded as a "sheet". For purposes of this invention, both thin film and sheet are included.
Thus, plastic material in accordance with this invention may have a thickness in the web area between the ribs from about 1 mil (or less) up to about 80 mil, and a thickness through the ribs of about 3 to about 500 mil, depending on the ultimate use of the material. For example, lightweight drop cloths, mulching film, vapor barriers and the like would normally be constructed of thin film plastic material. Outdoor tarpaulins and the like would typically be constructed on thicker, flexible plastic sheet material. In all such cases, the problem of tearing is present and thus, this invention has equal applicability to both thin film and sheet plastic.
By providing integrally formed ribs along one or more surfaces of the film of sheet material, tears are prevented, or at the very least inhibited, from propagating across the sheet, and, at the same time increased strength is obtained as well.
Other objects and advantages of the subject invention will become apparent from the detailed description which follows.